Moreover, RNA-seq showed that ER-positive breast cancer cells expressing ESR1-e6>YAP1, ESR1-e6>PCDH11X, ESR1-e6>SOX9 and ESR1-e6>ARNT2-e18 fusions upregulated the same cluster of ER target genes that were observed in the control cells stimulated by estradiol and drove constitutive expression of these ER target genes in the absence of estrogen. The gene discussed is ESR1; the disease is breast cancer.